The art of immobilizing a fractured bone in order to promote healing has been practiced for centuries. Starting from simple splints and sometimes rather unsanitary bandages, the invention of the plaster cast started a new era of orthopaedic medicine. Today, the heavy plaster casts are gradually replaced by lighter fibre glass alternatives. Further, in addition to purely external splints and casts, a variety of internal support structures are widely used. Such support structures include splints affixed directly to the fractured bone, pins and screws used to hold parts of the bone together during healing and to strengthen the site of the fracture. Further examples include plates, perforated scaffolds, intramedullar pins and screws, etc. These can be made of an inert material, such as titan, ceramic, or surgical steel, or made from a material which is resorbed or integrated in the body. Alternatively, the support structure is surgically removed when the fracture is fully healed.
Another group of devices, particularly relevant for the present invention, are mechanical devices which are mainly situated outside the body, but which engage the bones inside the body. The simplest form of such devices is a splint in the shape of a metal rod on the outside of the body, fixed to pins or screws anchored in the bone, and protruding through the skin. More complicated apparatuses include means for adjusting the position of the bones, for example applying tension to the fracture in order to align a complicated fracture, promote healing or to induce bone lengthening, a technique called distraction osteogenesis.
One example of external devices or fixtures for bone lengthening or reshaping is the so called Ilizarov apparatus, originally developed in the 1950s in the Sovjet Union, and introduced in Europe in the 1980s. In summary, this is an external fixture attached to the bone through the skin and tissues of the patient, and used in a surgical procedure that can be used to lengthen or reshape bones. Fixtures of this type are often used to treat complex fractures, such as open bone fractures, where conventional treatment techniques cannot always be used. It can also be used to treat infected non-unions of bones not amenable with other techniques. This and similar fixtures are also used for correcting deformities. For more information see e.g. Snela et al., 2000.
Another fixture is the Taylor Spatial Frame (TSF), an external fixator sharing a number of components and features of the Ilizarov apparatus. The TSF is a hexapod device consisting of two rings made of aluminium connected together by 6 struts. Each strut can be independently lengthened or shortened. When the apparatus is connected to a bone by wires or half pins, the attached bone can be manipulated in 6 axes (anterior/posterior, varus/valgus, lengthen/shorten.) Both angular deformities and translational deformities can be corrected with the TSF. It is used in both adults and children. It is used for the treatment of acute fractures, mal-unions, non uniona and congenital deformities. It can be used on both the upper and lower limbs. Specialised foot rings are also available for the treatment of complex foot deformities.
Once attached to the bone, the deformity is characterised by studying the postoperative x-rays. The angular and translational deformity values are then entered into specialised software along with parameters such as the ring size and initial strut lengths. The software then produces a “prescription” of strut changes that the patient follows. The struts are adjusted every day by the patient. Typically, correction of the bone deformity will take 3 to 4 weeks. Once the deformity has been corrected, the frame is then left on the leg whilst the bone heals, typically this will take 3 to 6 months, depending on the nature and degree of deformity.
Apparatuses of this kind may also be used for the lengthening of bones. This procedure consists of an initial surgery, during which the bone is surgically fractured and the ring apparatus is attached. As the patient recovers, the fractured bone begins to grow together. While the bone is growing, the frame is adjusted by means of turning the nuts, thus increasing the space between two rings. As the rings are connected to opposite sides of the fracture, this adjustment, done daily, moves the slowly healing fracture apart by approximately one millimeter per day. The incremental daily increases result in a considerable lengthening of the limb over time. Once the lengthening phase is complete, the apparatus stays on the limb to facilitate healing. The patient can move about on crutches and pain is lessened. Once healing is complete, a second surgery is necessary to remove the ring apparatus. The result is a limb that is significantly longer. Additional surgery may be necessary, in the case of leg lengthening, to lengthen the Achilles tendon to accommodate the longer bone length. The major advantage of this procedure is that the patient can remain active during the procedure, as the apparatus provides complete support while the bone is recovering. Patient activity and well-being is known to accelerate recovery.
While these external fixtures are minimally invasive (no large incisions are made) they are not free of complications. Pain is common and can be severe, but is treatable with analgesics. Careful attention to daily cleaning and hygiene is necessary to prevent pin site infection. Other complications include swelling and muscle transfixion. The external fixtures are also bulky, causing inconvenience and attracting unwanted attention in daily life.
There are examples of implantable devices, such as the implantable limb lengthening nail driven by a shape memory alloy disclosed in U.S. Pat. No. 5,415,660. This disclosure concerns an intramedullar nail consisting of an inner cylinder and an outer cylinder enclosing a drive means employing a shape memory alloy. This cylinder is attached to the bone by proximal and distal interlocking bolts, affixed from the outside of the bone, penetrating the bone, e.g. in the area of the epiphysis and the diaphysis, according to the figures in U.S. Pat. No. 5,415,660.
Another example of the background art is the tibial osteotomy fixation device of U.S. Pat. No. 5,827,286, comprising two plate members, telescopically movable in relation to each other, and a ratchet mechanism allowing movement in one direction only. This device is adapted for being attached to the outside of a bone, and affixed with bone screws.
U.S. 2005/0055025 A1 discloses various skeletal implants, connectable to joints or bones, suggesting a mechanism that initially is very rigid and absorbs external chock or stress thus protecting for example a graft or fracture during healing. It is suggested that this mechanism then progressively allows more movement, as the graft or fracture heals.
EP 0 432 253 discloses an intramedullary nail comprising a proximal and a distal end, and a mechanical, pneumatic, hydraulic, electrical or electromagnetic drive for rotating a rod inside said nail, for longitudinally expanding said nail. The nail has securing holes for engaging fastening nails or bolts, to be arranged transversally through the bone and intramedullary nail.
U.S. Pat. No. 5,156,605 concerns medical equipment for use in orthopaedics and traumatology, and is in particular directed to drive systems for a compression-distraction-torsion apparatus. One embodiment concerns an intramedullary device, fully implantable in a patient's bone, and including a motor drive, controller and battery functions, as well as radio frequency or electromagnetic field signals to allow a physician to adjust the rate and rhythm of distraction from outside the body. The device is shown anchored to the bone using nails or bolts penetrating the diaphysis and both end portions of the device.
Another problem associated with known devices is that the tension needs to be adjusted daily, either by the patient themselves, or by medical personnel. When the patient has the responsibility for adjusting the apparatus, there is a risk of poor compliance, due to pain or psychological discomfort.
Further, as there are indications that intermittent loading (Consolo et al., 2006), cyclic distraction and compression (Hente et al., 2004) and even oscillating forces promote osteogenesis and the differentiation of osteoblasts (Gabbay, 2006), the traditional mechanical devices leave room for improvements.
One objective of the present invention is to overcome the problems associated with known external and internal mechanical fixtures and splints.
Another objective is to make available new methods and devices for treatments involving distractive osteogenesis, both for therapeutic and cosmetic purposes.
Further objectives of the invention, as well as advantages associated with embodiments of the invention will become evident to a skilled person upon a closer study of the present description, non-limiting examples, claims and drawings.